1. Technical Field
The present disclosure relates to a barometric-pressure-sensor device having an altimeter function and an altimeter-setting function and to such a device designed to be integrated in portable electronic devices.
2. Description of the Related Art
There is an increasing use of electronic devices in the field of sports training. For example, electronic barometric altimeters are used for applications of mountain climbing and the like, in which the continuous monitoring of the altitude is of paramount importance.
In particular, electronic barometric altimeters are known including a pressure sensor, and a microprocessor control and processing circuit, designed to acquire and process pressure signals supplied by the pressure sensor for determining altitude information.
Portable electronic devices are also known, such as, for example, mobile phones, satellite navigators or wrist watches, provided with a barometric-altimeter function. These devices include, for this purpose, a pressure sensor (for example, a pressure sensor of a microelectromechanical (MEMS) type, as illustrated in FIG. 1), supplying to a microprocessor of the portable electronic device barometric-pressure detection signals. The microprocessor, in addition to controlling the general operation of the corresponding portable electronic device, processes the barometric-pressure detection signals for determining the altitude information.
FIG. 1 shows, by way of example, a known piezoresistive pressure sensor of a MEMS type. The use of this sensor in the aforesaid portable electronic devices can prove advantageous, given its small size.
In detail, the pressure sensor 1 includes: a substrate 2 made of semiconductor material (typically silicon); a buried cavity 3, contained and insulated within the substrate 2; and a flexible membrane 4, suspended over the buried cavity 3 and bending in the presence of external mechanical stresses. Piezoresistive elements 5, connected in a Wheatstone-bridge configuration, are diffused in a surface portion of the flexible membrane 4 and contacted by metal regions 6 (which enable electrical connection of the pressure sensor 1 from the outside). The pressure sensor 1 may, for example, be manufactured as described in European patent application No. EP-A-1 577 656, filed in the name of the present applicant.
In use, the top side of the flexible membrane 4 (i.e., the side opposite to the buried cavity 3) is set in communication with the outside environment. Consequently, the flexible membrane 4 is deformed as a function of the difference between the atmospheric pressure and the pressure present within the buried cavity 3, and this deformation causes unbalancing of the Wheatstone bridge formed by the piezoresistive elements 5; the desired pressure measurement is obtained from the unbalancing of the Wheatstone bridge.
The previously described known devices have some disadvantages.
In particular, given that the corresponding microprocessor carries out the whole processing of the detection signals supplied by the pressure sensor 1 for altitude calculation, it is not possible to place the microprocessor in stand-by mode for reducing its power consumption, without forgoing the altimetric measurement function. In this regard, it is known that power consumption issues are particularly relevant in portable electronic devices.
In addition, microprocessors of portable electronic devices provided with the barometric-altimeter function are designed to perform for the most part of their operating period procedures for management of the general operation of the portable electronic devices. Consequently, processing of the detection signals supplied by the pressure sensor 1 has a low priority, causing a delay in the determination of the altitude information; this determination is in any case performed with an increase in the computational burden for the microprocessor, causing a degradation of the performance of the associated portable electronic device.
Moreover, microprocessors of portable electronic devices are often of a dedicated type, incorporated in ASICs (Application-Specific Integrated Circuits). Their operation is optimized for carrying out certain operations for which they have been designed, typically different from the ones linked to altimetric detection. This entails a considerable inefficiency in terms of time and computational load.
Finally, communication of the barometric-pressure detection signals from the pressure sensor 1 to the corresponding microprocessor can cause degradation of the signal quality, with a consequent increase in the electrical noise. In fact, these signals typically have a rather low amplitude, and often the portable electronic devices are subject to, or generate, electromagnetic fields that may degrade the signal quality.